From bcdd228f90b3e9e428b584814e7d52627616456a Mon Sep 17 00:00:00 2001
From: James M Snell <jasnell@gmail.com>
Date: Mon, 7 Jan 2019 11:36:35 -0800
Subject: perf_hooks: implement histogram based api

Add a sampling-based event loop delay monitor.

```js
const { monitorEventLoopDelay } = require('perf_hooks');

const h = monitorEventLoopDelay();

h.enable();

h.disable();

console.log(h.percentiles);
console.log(h.min);
console.log(h.max);
console.log(h.mean);
console.log(h.stddev);
console.log(h.percentile(50));
```

PR-URL: https://github.com/nodejs/node/pull/25378
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
---
 lib/perf_hooks.js | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 68 insertions(+), 1 deletion(-)

(limited to 'lib/perf_hooks.js')

diff --git a/lib/perf_hooks.js b/lib/perf_hooks.js
index 583ffb56ca..b1d634bf3c 100644
--- a/lib/perf_hooks.js
+++ b/lib/perf_hooks.js
@@ -1,6 +1,7 @@
 'use strict';
 
 const {
+  ELDHistogram: _ELDHistogram,
   PerformanceEntry,
   mark: _mark,
   clearMark: _clearMark,
@@ -35,6 +36,8 @@ const { AsyncResource } = require('async_hooks');
 const L = require('internal/linkedlist');
 const kInspect = require('internal/util').customInspectSymbol;
 
+const kHandle = Symbol('handle');
+const kMap = Symbol('map');
 const kCallback = Symbol('callback');
 const kTypes = Symbol('types');
 const kEntries = Symbol('entries');
@@ -545,9 +548,73 @@ function sortedInsert(list, entry) {
   list.splice(location, 0, entry);
 }
 
+class ELDHistogram {
+  constructor(handle) {
+    this[kHandle] = handle;
+    this[kMap] = new Map();
+  }
+
+  reset() { this[kHandle].reset(); }
+  enable() { return this[kHandle].enable(); }
+  disable() { return this[kHandle].disable(); }
+
+  get exceeds() { return this[kHandle].exceeds(); }
+  get min() { return this[kHandle].min(); }
+  get max() { return this[kHandle].max(); }
+  get mean() { return this[kHandle].mean(); }
+  get stddev() { return this[kHandle].stddev(); }
+  percentile(percentile) {
+    if (typeof percentile !== 'number') {
+      const errors = lazyErrors();
+      throw new errors.ERR_INVALID_ARG_TYPE('percentile', 'number', percentile);
+    }
+    if (percentile <= 0 || percentile > 100) {
+      const errors = lazyErrors();
+      throw new errors.ERR_INVALID_ARG_VALUE.RangeError('percentile',
+                                                        percentile);
+    }
+    return this[kHandle].percentile(percentile);
+  }
+  get percentiles() {
+    this[kMap].clear();
+    this[kHandle].percentiles(this[kMap]);
+    return this[kMap];
+  }
+
+  [kInspect]() {
+    return {
+      min: this.min,
+      max: this.max,
+      mean: this.mean,
+      stddev: this.stddev,
+      percentiles: this.percentiles,
+      exceeds: this.exceeds
+    };
+  }
+}
+
+function monitorEventLoopDelay(options = {}) {
+  if (typeof options !== 'object' || options === null) {
+    const errors = lazyErrors();
+    throw new errors.ERR_INVALID_ARG_TYPE('options', 'Object', options);
+  }
+  const { resolution = 10 } = options;
+  if (typeof resolution !== 'number') {
+    const errors = lazyErrors();
+    throw new errors.ERR_INVALID_ARG_TYPE('options.resolution',
+                                          'number', resolution);
+  }
+  if (resolution <= 0 || !Number.isSafeInteger(resolution)) {
+    const errors = lazyErrors();
+    throw new errors.ERR_INVALID_OPT_VALUE.RangeError('resolution', resolution);
+  }
+  return new ELDHistogram(new _ELDHistogram(resolution));
+}
+
 module.exports = {
   performance,
-  PerformanceObserver
+  PerformanceObserver,
+  monitorEventLoopDelay
 };
 
 Object.defineProperty(module.exports, 'constants', {
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